This invention relates to integrated circuit processing. More particularly the invention relates to a polishing pad for use in chemical mechanical polishing of integrated circuit substrates.
Chemical mechanical polishing is used to planarize substrates, such as semiconductor substrates. Planarization is often performed between process steps to remove unwanted material and to reduce problems in step coverage during subsequent processing. Typically, chemical mechanical polishing is performed after circuit devices are partially formed on the substrate, but before the substrate is diced and the devices on the substrate are separated one from another.
During chemical mechanical polishing, a polishing pad is brought into contact with a surface of the substrate where devices are formed. A polishing slurry may be applied between the polishing pad and the substrate, and the substrate and pad are moved relative to each other, typically by spinning the pad in relation to the substrate. The slurry acts upon the substrate to both chemically etch and mechanically wear the surface of the substrate. The movement between the substrate and pad helps provide a uniform removal of material at the surface of the substrate.
Great care must be taken during chemical mechanical polishing to ensure that the substrate layer being planarized is thinned to within a predetermined range, or else devices formed in the layer may not function properly. Thus, it is typically desired to remove material evenly across the surface of the substrate during planarization. When the surface of an incoming substrate has a non flat profile, it is difficult to maintain even material removal across the surface of the substrate during polishing. For example, prior to planarization, an incoming substrate may have a surface profile which is higher on the edges and lower in the center. In this situation, it may be desirable to remove more material at the edges of the substrate than is removed near the center of the substrate. Generally, to remove more material at the edges than at the center, the polishing rate distribution must be adjusted to provide a higher polishing rate at the edges of the substrate than at the center.
Prior attempts at adjusting the polishing rate distribution in a chemical mechanical polishing process have been cost prohibitive and difficult to implement.
What is needed, therefore, is an uncomplicated and cost effective solution for adjusting the polishing rate distribution of a chemical mechanical polishing pad to account for non flat surface profiles on incoming substrates, such as those used for integrated circuits.
The above and other needs are met by a polishing pad for use in chemical mechanical polishing of a substrate. The polishing pad comprises a substantially flat disk having a polishing surface for contacting the substrate. The polishing surface, which has a central region and a peripheral region, is segmented by a set of substantially parallel linear grooves. The grooves include central grooves which traverse the central region of the polishing surface, and peripheral grooves which traverse the peripheral region of the polishing surface. The central grooves have central groove dimensions, including a central groove width and pitch, and the peripheral grooves have peripheral groove dimensions, including a peripheral groove width and pitch.
According to the invention, at least one of the central groove dimensions, such as either or both of the width or the pitch, is different from the corresponding peripheral groove dimension. This difference in groove dimensions from the center to the edge of the polishing surface introduces a difference in the polishing surface area provided near the peripheral region of the pad as compared to the central region of the pad. As the polishing pad spins in relation to the substrate being processed, the variation in polishing surface area across the polishing surface results in a difference in the rate of material removal near the periphery of the substrate as compared to the rate of material removal near the substrate center. Thus, the invention provides a radial variation in the polishing rate distribution across the polishing surface of the pad by providing a corresponding variation in the width or pitch of the grooves in the polishing surface.
In a most preferred embodiment of the invention, the grooves include a first set of substantially parallel linear grooves directed in a first direction and a second set of substantially parallel linear grooves directed in a second direction that is different from the first direction. The first set of grooves includes first central grooves and first peripheral grooves. The first central grooves, which traverse the central region of the polishing surface, have first central groove dimensions, including a first central groove width and pitch. The first peripheral grooves, which traverse the peripheral region of the polishing surface, have first peripheral groove dimensions, including a first peripheral groove width and pitch.
The second set of grooves includes second central grooves and second peripheral grooves. The second central grooves, which traverse the central region of the polishing surface, have second central groove dimensions, including a second central groove width and pitch. The second peripheral grooves, which traverse the peripheral region of the polishing surface, have second peripheral groove dimensions, including a second peripheral groove width and pitch. In preferred embodiments of the invention, at least one of the first central groove dimensions, such as one or both of the width or the pitch, is different from the corresponding first peripheral groove dimension, and at least one of the second central groove dimensions is different from the corresponding second peripheral groove dimension.